1. Field
The present disclosure generally relates to direct digital manufacturing techniques, especially additive methods, and deals more particularly with a method and apparatus for manufacturing fiber reinforced polymeric resin parts, and to a material mixture that may used to build the parts.
2. Background
Direct digital manufacturing (DDM), now referred to as Additive Manufacturing (AM), is a process that creates physical parts directly from a 3D CAD (computer aided design) file using computer controlled additive fabrication techniques. Common additive manufacturing techniques include stereolithography (SLA), fused deposition modeling (FDM), selective laser sintering (SLS) and three dimensional printing (3DP), to name a few. Each of these processes builds a three dimensional solid part, layer-by-layer, by locally fusing or curing building materials that may be in powder or liquid form. For example, the SLA process builds part a layer at a time using a UV laser and a vat of UV-curable liquid photopolymer resin. For each layer, the laser traces a part cross section pattern on the surface of the liquid resin based on a 3D CAD data model of the part. Exposure to the UV laser light cures and solidifies the pattern traced on the resin and adheres it to the layer below. After a pattern has been traced, an elevator platform descends by a single layer thickness, and a resin-filled blade sweeps across the part section, recoating it with fresh material. The process continues layer by layer until the part is complete.
SLS uses a high power laser to fuse small particles of plastic or metal, ceramic or glass powders into a mass that has a desired three dimensional shape. The laser selectively fuses the powdered building material by scanning cross sections generated from a 3D digital description (CAD model) of the part on the surface of a powder bed. After each cross section is scanned, the powder bed is lowered by one layer thickness, a new layer of material is applied on top, and the process is repeated until the part is complete.
The 3DP process uses a slicing algorithm to draw detailed information for each layer of a CAD model of the part. Each layer begins with a thin distribution of powder spread over the surface of a powder bed. Using a technology similar to ink-jet printing, a binder material selectively joins particles where the object is to be formed. A piston that supports the powder bed and the part-in-progress lowers so that the next powder layer can be spread and selectively joined. Following heat treatment, the unbound powder is removed, leaving the fabricated part.
In order to strengthen parts produced by additive manufacturing techniques, reinforcing particles, typically short milled or chopped fibers, have been introduced into the powders or liquid resins used to build the parts. However, the fibers are randomly distributed throughout the powder or resin matrix and have random individual orientations. Consequently, these fiber reinforcements yield a highly anisotropic reinforcement relative to the axis of the machine on which they are built.
Accordingly, there is a need for a method and apparatus for direct digital manufacturing of fiber reinforced parts in which the reinforcing fibers may be selectively oriented to provide isotropic reinforcement and directional strength in the part. There is also a need for a method and apparatus that position and/or align short reinforcing fibers or other particles in building materials used in various additive manufacturing processes.